This invention relates to solar hot water heating systems of the general type shown in Bottum U.S. Pat. No. 4,120,289 and is closely related to the invention described in allowed application Ser. No. 118,486, filed Feb. 4, 1980, now U.S. Pat. No. 4,296,729 by George H. Cooper, the disclosures of which are hereby incorporated by reference.
In solar hot water heating systems which employ a circulating heat transfer medium, which may be a phase-change medium, heated in the collector and cooled in a heat exchanger, giving up its heat to water in a water heating tank, and then returned to the collector, there is often produced more hot water than can be conveniently used or stored at the time. Such systems are often installed in existing homes which already have a hot water heating tank heated by electricity or some other means.
Furthermore, in those systems which employ a phase change heat transfer medium which evaporates in the collector and condenses to liquid form in the heat exchanger, it is desirable that the solar collector, in order to prolong its life, not be permitted to stagnate without the circulation of the medium. Such stagnation will occur if the heat transfer circulating system shuts down because of overheating. Such shut down can occur due to the operation of a pressure or temperature actuated valve, such as shown in Bottum U.S. Pat. No. 4,203,422, which operates to prevent overheating the medium.
An object of the invention is to provide means for cooling the system by releasing hot water from the water heating tank and replacing it with cold water thereby preventing overheating of the heat transfer medium and corresponding stagnation of the collecting panels.
Another object of the invention is to permit utilization of the surplus hot water thus generated in the solar heating tank by feeding it to an existing back-up hot water heating tank displacing water released therefrom.
A still further object is to provide such a system which is operated by the pressure of a circulating phase-change medium without any requirement for external power, pumps or the like.